Regional and Racial Differences in Venous Thrombosis in the United States: The Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study

Venous thrombosis (VTE) is thought to be more common in African-origin (black) than Caucasian-origin (white) Americans, however most prior studies are based on administrative databases, are limited in geographic scope, or have few blacks. Studies of VTE with diverse racial and geographic participants and validated VTE events are lacking.

Between 2003–07, 30,239 participants were enrolled in REGARDS, 55% were female, 41% were black, and 56% lived in the southeast (by design). Possible VTE events were identified by telephone interviews, review of reported hospitalizations, and review of deaths. VTE events were validated by physician review of hospital records, outpatient notes, imaging studies, and death records. VTE incidence rates by race and region controlling for age and sex were estimated using Poisson regression and racial and regional differences in VTE were evaluated using Cox proportional hazard models controlling for age, sex, region, obesity status, education, and income.

Among 27,807 individuals free of VTE at baseline, 268 incident VTE events occurred over a mean of 4.7 ± 1.6 years (Table). Blacks and whites had the same age and sex-adjusted VTE incidence (1.8 per 1000 person-years). When stratified by region, blacks living in the southeast had a higher incidence of VTE than whites (2.2 vs. 1.7 per 1000 person-years), while this was not the case in the rest of the US (1.5 vs. 2.0 per 1000 person-years) (Table). This difference in associations by race and region was statistically significant, such that the HR for blacks compared to whites was higher in the southeast (1.3) than in the rest of the country (0.8) even after adjusting for income, education, and obesity (all p-interaction ≤ 0.03) (Table). Further, blacks in the southeast had a higher VTE risk than blacks in the rest of the US (HR 1.5; 95% CI 1.0, 2.3) while there was no geographic disparity for whites (HR 0.8; 95% CI 0.6, 1.1) for the southeast vs. rest of the country.

For the first time, we demonstrate that region of residence significantly influences racial differences in VTE. Prior studies of racial differences in VTE have used administrative databases or studied blacks primarily from the southeast. In REGARDS, blacks in the southeast have higher rates of VTE compared to blacks in the rest of the US, and this is not explained by differences in income, education, and obesity. Whether these findings are due to differences in quality of care, genetic admixture, or novel VTE risk factors needs further study.

Cushman:Beckman: Honoraria.